1. Field of the Invention
The present invention relates to a bus system for the transfer of data within a master-slave system. It also refers to a method of transmitting, in particular, digital data by means of such a bus system.
2. Description of the Related Art
A bus system serves for the transfer, in particular, of digital data for the setting and/or testing of the state of different functional subunits. For this purpose, the bus system connects the functional subunits together, one of which subunits is a master while the others are slaves (single master bus). The functional subunits or slaves are not only frequently located on different circuit boards but, as a rule, also have interfaces for different types of transfer. Thus, some of the slaves may have an interface for a parallel data transfer, while each of the other slaves has an interface for a serial data transfer. Furthermore, the slaves or their interfaces may be designed for different directions of transfer, i.e. bidirectional or unidirectional and for either write access or read access.
Within a high frequency (HF) transceiver (radio-frequency unit, RFU) of a base station (Base Transceiver Station, BTS) for mobile communication in accordance with the GSM standard (Global Systems for Mobile Communication), each slave however is generally connected via a direct physical connection to the master for the transfer of control and status data, so that the master can write (send) data to each slave and read (receive) data from it. In such a star-shaped structure consisting of point-to-point connections, the master or its controlling processor has a separate interface for each subunit or each slave. This, however, results in a particularly high load on the processor upon regular activating of the different interfaces. Furthermore, the connecting of the slaves to the master is particularly difficult. Changes in individual subunits or an expansion of the system by additional subunits is not possible, or possible only at considerable expense, due to the necessary adaptations within the system.
Upon the use of a parallel data bus, the connecting of a slave having a serial interface requires additional circuits for adaptation to the bus system. Similarly, upon the use of a serial data bus, the connection of a slave with parallel interface requires additional circuits for adaptation to the bus. The use of additional circuits and signal lines results in a considerable expense.